Inscuteable and staufen mediate asymmetric localization and segregation of prospero RNA during Drosophila neuroblast cell divisions

When neuroblasts divide, inscuteable acts to coordinate protein localization and mitotic spindle orientation, ensuring that asymmetrically localized determinants like Prospero partition into one progeny. staufen encodes a dsRNA-binding protein implicated in mRNA transport in oocytes. We demonstrate that prospero RNA is also asymmetrically localized and partitioned during neuroblast cell divisions, a process requiring both inscuteable and staufen. Inscuteable and Staufen interact and colocalize with prospero RNA on the apical cortex of interphase neuroblasts. Staufen binds prospero RNA in its 3'UTR. Our findings suggest that Inscuteable nucleates an apical complex and is required for protein localization, spindle orientation, and RNA localization. Stau, as one component of this complex, is required only for RNA localization. Hence staufen also acts zygotically, downstream of inscuteable, to effect aspects of neuroblast asymmetry.